For drought watchers, it has become known as the May miracle.
At a time when water levels in Lake Mead were getting so low that officials prepared for drastic cutbacks, it started raining. A series of powerful storms pummeled the mountains that feed the Colorado River, a key source of water for California, Arizona and Nevada.
Water from the rain and snow flowed down the river and into reservoirs that are essential to modern life in the American West.
Lake Mead, where the water level this spring had fallen to lows not seen since Hoover Dam was built in the 1930s, began filling up again — enough to avoid the first cutbacks ever imposed in water deliveries, which the public had been warned could happen next year.
"It's taken us out of that potential red zone for this year. There is a 0% chance of a shortage" for next year, said Jeffrey Kightlinger, the Metropolitan Water District of Southern California's general manager. "That really good May offers us some breathing room."
Bill Hasencamp, the MWD's Colorado River program manager, was more blunt: "We dodged that bullet."
Had it not been for those storms, Southern California could have faced 30% to 40% reductions in imported water, Kightlinger said.
That's because Nevada and Arizona wouldn't have been as willing to lend California their unused river water if a shortage affects them.
Southern California is already draining its largest reservoir, Diamond Valley Lake, to keep faucets flowing in Los Angeles. Without more loans of river water, Diamond Valley Lake could have been drained down to its emergency reserve by the end of the year.
"That would've been scary," Kightlinger said.
The May miracle was so stunning that some officials could not believe how much water was flowing into Lake Powell, the reservoir upstream from Lake Mead.
"We were on a roller coaster, emotionally," said Chuck Cullom of the Central Arizona Project, which manages a 336-mile aqueduct that delivers river water to most of Arizona's population. "It was exciting. And there was a lot of sense of relief."
The storms came as the jet stream — a powerful flow of winds that moves from west to east — bypassed much of California and slid into the Great Basin over Nevada and Utah. It then transformed into spinning vortexes of energy, known as a cutoff low, Colorado state climatologist Nolan Doesken said.
Beginning in late April, the vortexes were supercharged by subtropical moisture off Mexico's coasts, Doesken said.
The result? Six powerful storms moving slowly across the southern and central Rocky Mountains and dumping rain that was unprecedented in the modern historical record.
"By the end of May, it was like, 'Whoa! What did just happen?' " Doesken said.
The effect can be seen across Colorado. It is now one of the best rafting seasons in years on the upper Colorado River, Ryan Santilli of AVA Rafting said. In early June, the company had to bar young children from rafting as a safety precaution as late spring snows melted.
"We did see a ton more snow ... which really helped put the season over the edge," Santilli said. "We're on a roll."
The storms were also responsible for deadly flooding in Texas and Oklahoma.
Global warming is playing a role in why storms are getting wetter while droughts are getting more severe, said Jake Crouch, climate scientist for the National Oceanic and Atmospheric Administration office in Asheville, N.C.
As temperatures rise, the amount of moisture in the air also rises, Crouch said. So whenever it rains or snows, more moisture is being squeezed out of the atmosphere at that particular location — meaning "there's less available somewhere else," Crouch said.
But the storms don't resolve the long-term problems that California, Nevada and Arizona face in their water supply from the Colorado River.
For decades, Lake Mead's water reserves, even in previous droughts, had remained generally stable because of low demand.
It wasn't until 2000 that demand for river water soared just as a 15-year drought along the Colorado River basin began, Hasencamp said. Since then, we have been taking water out of the bank.
"Unfortunately, that's the reality of the Colorado River: There is a long-term imbalance that we can't continue to operate in the future as we have in the past," Hasencamp said.
The Colorado River was divvied up based on the amount of water that flowed through it in the early 20th century, years that scientists now realize were wetter than average. Global warming will probably worsen the situation, Hasencamp said.
"Years like this — the Miracle May — helped us borrow time," he said. "But eventually, there's not going to be enough water to meet all demands."
It's not only California, Arizona and Nevada that are worried about shrinking water levels in the nation's two largest reservoirs.
A shortage at Lake Mead could force further draining of Lake Powell, which could eventually affect the water supply in Colorado, Utah, Wyoming and New Mexico, which must share river water with states further downstream, said James Eklund, who works to protect Colorado's interests on the Colorado River.
A shortage could create a catastrophic domino effect. If Lake Powell is drained too much, water won't be able to get into the pipes that power turbines that generate electricity at Glen Canyon Dam. That could raise electricity prices, Eklund said.
"It's kind of the — hang together, or we all hang separately — deal," Eklund said.
In the meantime, water agencies in Nevada and Arizona are closing in on talks to loan more river water to Southern California in exchange for promises to return it in later years, when they might need more insurance against drought.
"Once you go into shortage, I think the politics starts to take over," Kightlinger said. "When you're not in shortage, then I think us water managers can continue to work with each other."
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